Virtual Threads landed in Java 21 as a stable feature, and Spring Boot 3.2 added first-class support with a single property. The promise: write simple blocking code and get WebFlux-level throughput. The reality is mostly true — with some important exceptions. This article covers what Virtual Threads actually are, how to enable them in Spring Boot, real benchmark numbers, the three pitfalls that will silently destroy your performance, and a decision framework for when to use them (and when not to).